In Direct Imaging (DI) systems, a scanning beam is used to directly write an image, one or more pixels at a time onto an exposure surface such as a photoresist. The image is sometimes obtained by modulating the scanning beam with an Acoustic Optical Modulator (AOM) also called a Bragg cell. The AOM uses the acousto-optic effect to diffract and deflect light using sound waves (usually at radio-frequency) based on stored image data. Once modulated, scanning is typically provided in a raster pattern by reflecting the modulated beam off a multi-faceted rotating polygon as the exposure surface (or scanning beam) advances in a scan direction.
In some known systems, the Scophony scanning effect is used to minimize spatial blurring of a generated pattern caused by: a) a finite velocity of the acoustic wave in the modulator and b) a continuous nature of the laser illuminator. A requirement for the Scophony scanning effect is that the acoustic velocity of the sound wave in the AOM, increased by a magnification ratio of the optical system between the AOM and exposure surface, is equal to the scan speed of a writing spot on the exposure surface, but in the opposite direction. The Scophony scanning effect leads to “standing” data information on a predetermined place on the exposure surface.
U.S. Pat. No. 4,205,348 entitled “Laser scanning utilizing facet tracking and acousto pulse imaging techniques,” the contents of which is incorporated herein by reference, describes a method and apparatus for improving the efficiency and resolution of laser scanning systems using a multi-faceted rotating polygon as the scanner device. An acousto-optic Bragg cell is utilized as an active optical element to both modulate and deflect an incident laser beam so that the modulated beam is caused to track one facet of the scanner during a complete scan and to shift to the adjacent facet for the following scan. In order to provide facet tracking the acoustic carrier frequency must vary in time synchronization with the scanning action of the surface of the recording medium. It is described that imaging of the input electrical signal on the recording medium surface is accomplished without blurring, using the Scophony scanning effect by moving the image of the acoustic pulses at the surface of a recording medium at the same relative velocity, in the opposite direction, as the velocity of the laser recording, or write beam.
U.S. Pat. No. 5,309,178 entitled “Laser marking apparatus including an acoustic modulator,” the contents of which is incorporated herein by reference, describes a laser marking apparatus includes at least one laser beam source, a multichannel acoustic modulator defining a plurality of at least partially overlapping modulation regions, apparatus for directing at least one laser beam from the at least one laser beam source through the multichannel acoustic modulator such that each laser beam extends across at least two of the at least partially overlapping modulation regions, and imaging apparatus for directing light from the modulator to a laser marking image plane.
The laser beam source is operated in continuous wave mode. It is described that a Laser Diode (LD) is used as the laser beam source for scanning a recording medium with a material of high photosensitivity. Optionally, a pair of LDs, each with a corresponding driver, a retardation plate and a collimation lens is as the laser beam source. When employing the pair of LDs, the retardation plates rotate the polarization vectors of the LDs so that they can be combined without loss of energy by a polarizer beam splitter.
U.S. Pat. No. 6,770,866 entitled “Direct pattern writer,” the contents of which is incorporated herein by reference, describes an apparatus for scanning a beam across a surface including a scanner scanning a pulsed laser beam across a surface and a position indicator receiving an input from the pulsed laser beam at a plurality of locations across the surface, and outputting position indications indicating a position of said pulsed laser beam along said surface. The position indications are used to modulate data in apparatus for exposing patterns on surfaces, for example electrical circuit patterns on photosensitized surfaces. One use of such apparatus is the manufacture of electrical circuits. It is described that edge fixing is accomplished by employing the Scophony scanning effect.
U.S. Pat. No. 7,046,266 entitled “Scanner System,” the contents of which is incorporated herein by reference, describes a method of scanning for writing a pattern on a surface. The method includes providing a scanning beam comprised of a plurality of independently addressable sub-beams, an unmodulated energy of said scanning beam having a generally Gaussian profile; scanning the surface with said scanning beam a plurality of times, said sub-beams scanning the surface side-by side in the cross-scan direction, each said sub-beam being modulated to reflect information to be written; and overlapping the beams in successive scans in the cross-scan direction such that all written areas of the surface are written on during at least two scans. Modulation is provided by an acosto-optic modulator (Bragg cell). The Scophony effect is used to decrease or remove blur of generated edges in the scan direction of flying spot scanners.
There is also described a scanning apparatus with a beam comprising energy at two distinct spectral lines, modulated by data; and an optical system that receives the beam and focuses it on the surface, such that a pattern is written on the surface by the at least one beam and such that the energy at both spectral lines is focused on the surface at the same position. Focusing at the same position is provided by designing the entrance and exist faces of the AOM such that the difference in refraction for the two beams (at the different wavelengths) at the input and output faces is exactly equal and opposite to the difference in Bragg angles for the beams. Thus, the two beams which enter together, exit together.
U.S. Patent Publication No. 2007/0058149, entitled “Lighting System and Exposure Apparatus,” the contents of which is incorporated herein by reference, describes a method and apparatus for illuminating a recording medium with two dimensional array of semiconductor LDs. The two dimensional array of LDs are used to replace lower efficiency mercury lamps or excimer lasers. Diffused beams output from the two-dimensional array of LDs are converted into high-directivity beams with spread angles equalized circumferentially by two kinds of cylindrical lenses. Tilt in optical axis of individual beams due to misalignment with the center of the beam is corrected by a two dimensional array wedged glass. The beams are modulated with a two-dimensional light modulator such as a mask or a Digital Mirror Device (DMD) for maskless exposure.